Monoclonal antibodies have become an important class of therapeutic proteins. However, foreign immunoglobulins used in humans can elicit an anti-globulin response which may interfere with therapy or cause allergic or immune complex hypersensitivity. To avoid this problem, a monoclonal antibody may be “humanized,” and this is typically carried out by CDR grafting.
CDR's, also called hypervariable regions, are present in immunoglobulin light and heavy chains and are flanked by “framework” regions. CDR grafting was first described in Jones et al. ((1986) Nature 321:522-525). In this and later publications, the CDRs of three mouse antibodies were grafted onto the variable domain frameworks of the human immunoglobulin NEW (VH) and REI (VL). The resulting humanized antibodies had the same antigen specificity and a similar affinity as the parental murine monoclonal antibody (mAb) (Jones et al. supra; Verhoeyen et al. (1988) Science 239:1534-1536; Riechmann et al. (1988) Nature 332:323-327; U.S. Pat. No. 5,225,539).
CDR grafting has been described by Queen and coworkers who reported the humanization of four murine monoclonal antibodies (Queen et al. (1989) Proc. Natl. Acad. Sci. USA 86:10029-10033; Co et al. (1991) Proc. Natl. Acad. Sci. USA 88:2869-2873; Co et al. (1992) J. Immunol. 148:1149-1154; and U.S. Pat. Nos. 5,585,089; 5,693,761; and 5,693,762). Murine residues were inserted in the human framework in order to maintain affinity and, in each case the original antigen specificity was maintained. The affinities of the humanized antibodies ranged from ⅓ to 3 times of the parental unmodified murine antibodies.